Electronic devices continue to become smaller and more complex. As the complexity increases, there is a tendency for these devices to require more buttons, including entire alphanumeric character sets and as well as additional function-specific keys. Combination keypad locks are more difficult to pick when an increased number combinations are possible. Specific examples include: remote control units for complex tasks such as interactive television; cellular telephones and pagers with written communication capabilities; combination keypad lock interfaces; and wired telephones with peripheral control abilities.
Such devices are problematic because the human hand remains relatively constant in size while the componentry shrinks. The result is that the interface to the hand, the keypad, often dictates the smallest possible size of an electronic device. It is therefore increasingly important to minimize the size of the keypad without reducing the size of the keys smaller than the human hand may use comfortably.
Previous efforts to address this issue consist of the following:
Scale the Keypad Smaller
The most obvious way to increase the number of functions in a given area is to scale the keypad smaller reducing key cap size and decreasing the distance between key cap centers. This technique causes the user to feel constrained. Products which use small keypads suffer from the impression that they are toy-like, largely because, in fact, they are scaled for use by a child. Decreasing key cap size makes the keys less comfortable to a full-sized adult finger. Decreasing the distance between key cap centers increases the likelihood of accidental input. Decreasing the size of the legend reduces legibility and the ease of viewing. In these ways, this solution is workable but far from optimal.
Chorded keyboards
Chorded keyboards have a relatively small number of keys, often linearly disposed to conform with the resting position of the human hand, which operate in combination to form each input, offering 2 raised to the N number of different inputs where N is the number of keys. The primary problem with this solution is that it requires the user to memorize 2 N input combinations and to develop the necessary motor skills. While this is a workable solution for extremely dedicated users, it is impractical and requires an unrealistically large amount of practice for most.
Modal Solutions
There are a variety of solutions in which individual keys are given a plurality of functions: Time variance modality varies the time between key operations to define the output function. This is non-intuitive and severely restricts the pace at which an operator may work; Function key modality alters the functionality of the keystroke(s) which follow in a predetermined manner. While this is an extremely common technique, it has limitations. While a function key doubles the possible outputs of a keypad, it also doubles the number of keystrokes required. Further, it is impractical to reduce the dimension of the standard 10-key keypad or the space required by the 26 letters of the alphabet by implementing a function key solution because the characters of these sets are of near-equal significance. Force sensitive modality incorporates a plurality of force-levels to a single button, and thereby a plurality of functions. Tests show that there is a wide variation in the forces naturally applied by users and wide variations in the levels of force sensitivity between users. The solution is highly non-intuitive. For these reasons, force sensitive keys are not widely applicable, nor desirable.
What is desirable is a keypad which increases the number of functions which can be output from a given number of keys, without compromising the ergonomic advantages of full-size and individually operable key caps. It is further desirable to not require any learning or practice. The keypad would be non-modal to eliminate the confusion and errors commonly associated with modalities. Each output function would permanently correlate with a single key cap location. The identifying legends would be full-size for easy identification. Functions would be accessible by a single finger push. The keypad would be small without being toy-like because it is designed to accommodate a full-size human finger. Ideally a compact keypad would effect full-sized key caps with on center distances smaller than full-sized key cap dimensions allow.